Re: [PATCH 05/11] mm: Introduce arch_pgd_init_late()

[Linus Torvalds]

On Mon, Sep 21, 2015 at 11:23 PM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> Add a late PGD init callback to places that allocate a new MM
> with a new PGD: copy_process() and exec().
>
> The purpose of this callback is to allow architectures to implement
> lockless initialization of task PGDs, to remove the scalability
> limit of pgd_list/pgd_lock.

Do we really need this?

Can't we just initialize the pgd when we allocate it, knowing that
it's not in sync, but just depend on the vmalloc fault to add in any
kernel entries that we might have missed?

I liked the other patches in the series because they remove code and
simplify things. This patch I don't like.

There may be some reason we need it that I missed, and which makes me
go "Duh!" when you tell me. But please do tell me.

               Linus
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